Detection device and method of anodic oxide film

ABSTRACT

A device for detecting an anodic oxide film during an anodic oxidation treatment includes a container receiving an electrolyte therein, an aluminum sheet immersed in the electrolyte, a power source supplying a current to the aluminum sheet to form an anodic oxide film on the aluminum sheet, a data acquisition unit measuring a potential of the anodic oxide film at a time, a data processor unit calculating a differential value of the potential, and a display unit displaying a differential curve generated according to the differential values of the potentials at different times. The quality of the anodic oxide film can be judged by reading the shape of the differential curve.

BACKGROUND

1. Field of the Disclosure

The disclosure generally relates to detection devices and detectionmethods, and more particularly to a detection device and method fordetecting an anodic oxide film during an anodic oxidation treatment.

2. Description of Related Art

Anodic oxide films have drawn much attention for industrial andnanotechnology uses because of their unique pore formation capability,which not only increases corrosion resistance but has the added value ofenhanced cosmetic appearance. The anodic oxide film is composed of aporous layer. During an anodic oxidation treatment, a current density, abath temperature, and an acid concentration of an electrolyte mayinfluence a pore formation capability of the anodic oxide film. Forexample, a burnt film may be formed at a higher current density, andpitting and burning tend to occur at a lower acid concentration or whena concentration of a sulfate increases. However, to examine the textureof the anodic oxide film always involves the use of an electronicmicroscope and preparation of specimens, which is tedious and laborious.

For the foregoing reasons, there is a need in the art for a detectiondevice and method for detecting an anodic oxide film which overcome thelimitations described.

SUMMARY

According to the disclosure, a device for detecting an anodic oxide filmduring an anodic oxidation treatment includes a container receiving anelectrolyte therein, an aluminum sheet immersed in the electrolyte, apower source electrically connected to the aluminum sheet for supplyinga current to the aluminum sheet to cause an anodic oxide film to grow onthe aluminum sheet, a data acquisition unit measuring a potential of theanodic oxide film, a data processor unit calculating a first-orderdifferential value of the potential at a time, and a display unitdisplaying a first-order differential curve generated according to thedifferential values of the potentials at different times. During aperiod between the time when the potential of the anodic oxide filmreaches a maximum and the time when the potential of the anodic oxidefilm starts to become constant, if only one valley is formed on thefirst-order differential curve, the anodic oxide film is excellent;should there be more than one valleys formed on the first-orderdifferential curve, the anodic oxide film has a poor quality.

Other advantages and novel features of the disclosure will be drawn fromthe following detailed description of the exemplary embodiments of thedisclosure with attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a detection device according to anexemplary embodiment for detecting an anodic oxide film during an anodicoxidation treatment.

FIG. 2 is a flowchart of a detection method for detecting the anodicoxide film during the anodic oxidation treatment using the detectingdevice of FIG. 1.

FIG. 3 is a potential-time curve and an associated first-orderdifferential curve of the anodic oxide film formed by anodizing analuminum sheet in a sulfuric acid solution with a concentration of 15 wt% at a bath temperature of 293K and a current density of 15 mA/cm².

FIGS. 4-7 show microscopic images of the anodic oxide film of thealuminum sheet at different anodizing times under the condition of FIG.3.

FIG. 8 is similar to FIG. 3, but shows the potential-time curve and theassociated first-order differential curve of the anodic oxide filmformed by anodizing the aluminum sheet in a sulfuric acid solution witha concentration of 10 wt % at a bath temperature of 303K and a currentdensity of 27 mA/cm².

FIG. 9 shows a microscopic image of the anodic oxide film formed on thealuminum sheet under the condition of FIG. 8.

FIG. 10 shows the potential-time curve and the associated first-orderdifferential curve of the anodic oxide film formed by anodizing thealuminum sheet in a sulfuric acid solution with a concentration of 20 wt% at a bath temperature of 283K and a current density of 24 mA/cm².

FIG. 11 shows a microscopic image of the anodic oxide film formed on thealuminum sheet under the condition of FIG. 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a detection device for detecting an anodic oxidefilm in an anodic oxidation treatment includes a power source 1, a dataacquisition unit 8, a data processor unit 10, a display unit 11 and acontainer 14.

An electrolyte 6, such as a solution including sulfuric acid, phosphoricacid, chromic acid, and organic acid, is filled in the container 14. Thecontainer 14 is received in a constant temperature device 7 to maintaina constant anodizing temperature during the anodic oxidation treatment.An aluminum sheet 9 functions as an anode and has a bottom end extendinginto the electrolyte 6 and a top end electronically connected to apositive pole 2 of the power source 1. An aluminum post 4 functions as acathode and has a bottom end extending into the electrolyte 6 and a topend electronically connected to a negative pole 3 of the power source 1.Thus the power source 1 can supply a current to the aluminum sheet 9.The power source 1 can be adjusted to change a current density flowingthrough the aluminum sheet 9. A calomel electrode 5 is utilized as areference electrode. The calomel electrode 5 has a bottom end extendinginto the electrolyte 6, and a top end connected to a reference terminal82 of the data acquisition unit 8. An input terminal 81 of the dataacquisition unit 8 is connected to the top end of the aluminum sheet 9,an earth terminal 83 of the data acquisition unit 8 is connected to theground, and an output terminal 84 of the data acquisition unit 8 isconnected to an input terminal 13 of the data processor unit 10. Thedisplay unit 11 is connected to an output terminal 12 of the dataprocessor unit 10.

During the anodic oxidation treatment, the power source 1 supplies thecurrent to the aluminum sheet 9 to cause an anodic oxide film tocontinuously grow on the aluminum sheet 9 until reaching a quasi-steadystate. A pore formation capability of the anodic oxide film can bedetected during the anodic oxidation treatment according to a detectingmethod shown in FIG. 2. The detecting method mainly includes thefollowing steps: (a) obtaining different potentials U of the anodicoxide film at different anodizing times t by the data acquisition unit8, recording and processing the recorded potentials U and times t by thedata processing unit 10 to obtain a potential-time curve 20 anddisplaying the potential-time curve 20 by the display unit 11 which hasa potential-time coordinates; (b) differentiating the differentpotentials U at different times t by the data processing unit 10 toobtain first-order differential values U′ at different times t; (c)generating a first-order differential curve 21 by the data acquisitionunit 8 according to the first-order differential value U′ at differenttimes t and displaying the first-order differential curve 21 by thedisplay unit 11; and (d) judging the pore formation capability of theanodic oxide film according to a shape of the first-order differentialcurve 21. Details of the detection method will be expatiated withspecific anodic oxidation treatment examples as follows.

In one specific anodic oxidation treatment, the electrolyte 6 is asulfuric acid solution with a concentration of 15 wt %. The aluminumsheet 9 is anodized in the sulfuric acid solution at a bath temperatureof 293K and a current density of 15 mA/cm². The data acquisition unit 8measures the potential U of the anodic oxide film at a frequency f of100 Hz. The potential U of the anodic oxide film is converted to digitalsignal and sent to the data processor unit 10. The data processor unit10 records the potential U of the anodic oxide film at the anodizingtime t as U(t). Accordingly, the potential U of the anodic oxide film atthe anodizing time t−1 is recorded as U(t−1), and the potential U of theanodic oxide film at the anodizing time t+1 is recorded as U(t+1). Thenthe data processor unit 10 calculates the first-order differential valueU′ of the potential U according to a formula of U′=[U(t)−U(t−1)]*f. Thusa potential-time curve 20 is obtained according to the potentials U ofthe anodic oxide film at the anodizing times t, and a first-orderdifferential curve 21 is obtained according to the first-orderdifferential values U′ at the anodizing times t. Finally both of thepotential-time curve 20 and the first-order differential curve 21 aredisplayed on the display unit 11, as shown in FIG. 3.

The potential-time curve 20 and the first-order differential curve 21can be divided into four segments, which correspond to four stages ofthe growth of the anodic oxide film, i.e., a barrier layer formationstage, a nanopore initiation and growth stage, a pore widening stage,and a quasi-steady state stage. The four stages are divided by threeanodizing times, t_(U′max), t_(Umax), and t_(Uconst). The anodizing timet_(U′max) is the time that the first-order differential curve 21 has amaximum value: U′max. The anodizing time t_(Umax) is the time that thepotential-time curve 20 has a maximum value: Umax, and at this time, thefirst-order differential value U′ of the potential U is zero. Theanodizing time t_(const) is the time that the first-order differentialcurve 21 and the potential-time curve 20 start to become straight andhorizontal. In other words, from the anodizing time t_(const), thepotential U of the anodic oxide film is constant, the first-orderdifferential value U′ of the potential U is zero. The barrier layerformation stage is from the start of formation of the anodic oxide film(i.e., t=0) to the anodizing time t_(U′max). The nanopore initiation andgrowth stage is from t_(U′max) to t_(Umax). The pore widening stage isfrom t_(Umax) to t_(Uconst). After the anodizing time t_(Uconst) is thequasi-steady state stage. The pore formation capability of the anodicoxide film is judged according to an amount of valleys of thefirst-order differential curve 21 in the pore widening stage. If thefirst-order differential curve 21 has only one valley in the porewidening stage, the anodic oxide film formed on the aluminum sheet 9 isexcellent. In contrast, if the first-order differential curve 21 hasmore than one valleys in the pore widening stage, the quality of theanodic oxide film is poor.

Referring to FIG. 3 again, in the barrier layer formation stage, theanodic oxide film initially and continuously grows on the aluminum sheet9. The initially formed anodic oxide film significantly increases theelectric resistance of the aluminum sheet 9. The potential U of theanodic oxide film increases with the increase of the electricresistance. An increasing rate of the potential U of the anodic oxidefilm is more and more faster, and thus the first-order differentialvalue U′ of the potential U increases remarkably until reaching themaximum U′max. According to the first-order differential curve 21, themaximum first-order differential value U′max is about 3.96, and theanodizing time t_(U′max) is about 2.37s. In other words, a period forthe barrier layer formation stage is about 2.37s. An intersection pointA of the potential-time curve 20 with a vertical line of t=t_(U′max) isabout (2.37s, 10.08V), i.e., the potential U of the anodic oxide filmreaching 10.08V at the end of the barrier layer formation stage. FIG. 4shows the anodic oxide film formed on the aluminum sheet 9 in thebarrier layer formation stage at the anodizing time of about 2s, whichis substantially a barrier layer consisting mainly of amorphous typeoxide which is compact and free of pores.

In the nanopore initiation and growth stage, the potential U of theanodic oxide film continues to rise until reaching the maximum Umax.However, the increasing rate of the potential U of the anodic oxide filmin the nanopore initiation and growth stage is slower. As shown in FIG.3, the first-order differential value U′ of the potential U decreases tozero when the potential U of the anodic oxide film reaches the maximumUmax. A point B (8.51s, 25.54V) indicates the peak of the potential-timecurve 20, i.e., the maximum potential Umax of the anodic oxide film isabout 25.54V, and the anodizing time t_(Umax) is about 8.51s. Thenanopore initiation and growth stage is from 2.37s to 8.51s. In thisstage, initially, nanopores are formed on the surface of the anodicoxide film, which result in the decrease of the first-order differentialvalue U′ of the potential U. Then the current supplied by the powersource 1 to the aluminum sheet 9 for growing the anodic oxide filmthereon functions as a pore current and an anodic oxide film formationcurrent. The pore current increases because of growing of the nanopores,while the formation current decreases due to increase of the resistanceof the anodic oxide film. Finally affected by the pore current,nanopores persistently increase in size to become pores. FIG. 5 showsthe anodic oxide film formed on the aluminum sheet 9 in the nanoporeinitiation and growth stage at the anodizing time of about 6s, which hasa plurality of pores.

In the pore widening stage, the anodic oxide film continues to growthuntil it reaches the quasi-steady state at the anodizing timet_(Uconst). The pores of the anodic oxide film widen persistently andbecome apparent. According to the first-order differential curve 21 andthe potential-time curve 20 of FIG. 3, the anodizing time t_(Uconst) isabout 20.08s. At the anodizing time t_(Uconst), the potential Uconst ofthe anodic oxide film decreases to about 17.15V, as indicated by pointC. As shown in FIG. 6, the pores of the anodic oxide film at theanodizing time of about 12s are apparent. After the anodizing timet_(Uconst), i.e., in the quasi-steady state stage, the potential U ofthe anodic oxide film is constant, being 17.15V, and thus thefirst-order differential value U′ of the potential U is also constant,being zero. Both of the first-order differential curve 21 and thepotential-time curve 20 in the quasi-steady state stage after theanodizing time t_(Uconst) are straight and horizontal.

In the pore widening stage, the potential-time curve 20 declines, andthe potential U of the anodic oxide film decreases gradually form Umaxto U_(const). The first-order differential curve 21 goes from zero to aminimum, and then lifts to zero again when the potential U of the anodicoxide film reaches U_(const). One valley is formed in the pore wideningstage of the first-order differential curve 21 when the first-orderdifferential value U′ of the potential U reaches the minimum U′min,which is indicated by point D. The time t and the minimum U′min at thepoint D are about 10.27s and −1.71. According to the yardstick, if thefirst-order differential curve 21 has only one valley in the porewidening stage, the anodic oxide film formed in this specific anodicoxidation treatment that the aluminum sheet 9 is anodized in a sulfuricacid solution of 15 wt % concentration at a bath temperature of 293K anda current density of 15 mA/cm² has a good quality. FIG. 7 shows thepores of the anodic oxide film at the anodizing time of about 22s; it isobvious that the anodic oxide film has an excellent pore formation.

FIG. 8 shows the potential-time curve 22 and the first-orderdifferential curve 23 of a second specific anodic oxidation treatment.In this anodic oxidation treatment, the aluminum sheet 9 is anodized inthe electrolyte 6 with a concentration of 10 wt % at a bath temperatureof 303K and a current density of 27 mA/cm². It is obvious that thefirst-order differential curve 23 has two valleys in the pore wideningstage, and thus the anodic oxide film is poor in quality. As shown inFIG. 9, pitting is generated in the anodic oxide film, and thus the poreformation of the anodic oxide film is bad.

FIG. 10 shows the potential-time curve 24 and the first-orderdifferential curve 25 of a third specific anodic oxidation treatment. Inthe third specific anodic oxidation treatment, the aluminum sheet 9 isanodized in the electrolyte 6 with a concentration of 20 wt % at a bathtemperature of 283K and a current density of 24 mA/cm². Similar to FIG.8, the first-order differential curve 25 in FIG. 10 has more than onevalleys in the pore widening stage, and thus the anodic oxide film has apoor quality. As shown in FIG. 11, pitting also occurs in the anodicoxide film.

It is to be understood, however, that even though numerouscharacteristics and advantages of the disclosure have been set forth inthe foregoing description, together with details of the structure andfunction of the disclosure, the disclosure is illustrative only, andchanges may be made in detail, especially in matters of shape, size, andarrangement of parts within the principles of the disclosure to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

1. A method for detecting an anodic oxide film during an anodicoxidation treatment, comprising steps of: acquiring potentials of theanodic oxide film at different anodizing times by a data acquisitionunit; calculating differential values of the potentials at the differentanodizing times by a data processor unit; generating a differentialcurve according to the differential values of the potentials anddisplaying the differential curve on the display unit; and judging apore formation capability of the anodic oxide film according to a shapeof the differential curve.
 2. The method of claim 1, further comprisinggenerating a potential-time curve according to the potentials of theanodic oxide film at the different anodizing times, and displaying thepotential-time curve associated with the differential curve on thedisplay unit.
 3. The method of claim 2, wherein during a period of theanodizing times from a time when a corresponding potential of the anodicoxide film reaches a maximum to a time when a corresponding potential ofthe anodic oxide film starts to become constant, if only one valley isformed on the differential curve, the anodic oxide film is excellent,and if more than one valleys are formed on the differential curve, theanodic oxide film is bad.
 4. A device for detecting an anodic oxide filmduring an anodic oxidation treatment, comprising: a container receivingan electrolyte therein; an aluminum article extending into theelectrolyte; a power source electrically connected to the aluminumarticle for supplying a current to the aluminum article to cause ananodic oxide film to grow on the aluminum article; a data acquisitionunit measuring potentials of the anodic oxide film at different times; adata processor unit calculating differential values of the potentials atthe different times; and a display unit displaying a differential curvegenerated according to the differential vales of the potentials.
 5. Thedevice of claim 4, wherein the container is received in a constanttemperature device for maintaining a constant anodizing temperatureduring the anodic oxidation treatment.
 6. The device of claim 4, whereinthe power source can be adjusted to change a current density through thealuminum article.
 7. The device of claim 4, wherein the aluminum articleis connected to a positive pole of the power source, the device furthercomprising another aluminum article connected to a negative pole of thepower source, and a calomel electrode function as a reference electrode.8. The device of claim 7, wherein the calomel electrode has one endextending into the electrolyte, and another end connected to a referenceterminal of the data acquisition unit, an input terminal of the dataacquisition unit being connected to the aluminum article, and an outputterminal being connected to the data processor unit.
 9. The device ofclaim 7, wherein the data processor unit generates a potential-timecurve according to the potentials of the anodic oxide film at thedifferent times, and the display unit displays the potential-time curveassociated with the differential curve.
 10. The device of claim 4,wherein the electrolyte is a solution including one of sulfuric acid,phosphoric acid, chromic acid, and organic acid.